In general, a brake system is used to decelerate, stop, or park a moving vehicle.
A friction brake, which converts kinetic energy into thermal energy by using a frictional force and radiates the thermal energy to the air, is generally used in the brake system. Pads press both sides of a disk, which rotates together with a wheel, with hydraulic pressure, so that the friction brake implements a braking function.
The hydraulic brake implements braking by pressing the pads against the disk using hydraulic pressure. For this reason, the hydraulic brake cannot help having a complicated structure including a master cylinder that is operated by a booster for increasing a force applied to a pedal to generate hydraulic pressure, hydraulic pressure lines connected to a wheel cylinder, and various devices that control and assist the cylinders and lines. Accordingly, improvement in the stability of the hydraulic brake is limited due to the complicated structure and deterioration in the reliability of a braking performance, which is caused by use of hydraulic pressure.
Therefore, an electro wedge brake system has been being developed and applied so as to have a simple structure unlike the hydraulic brake, improve the reliability of a braking performance, implement a parking brake function, improve the responsiveness and performance of an ABS (Anti Brake System), and optimally control an integrated chassis.
The electro wedge brake (EWB) uses the following method when braking. That is, brake pads are pressed against the disk by a wedge assembly that is operated by an actuator, and frictionize the disk so as to implement a braking function.
In this case, even though the EWB uses a motor using a voltage of 12 V, the EWB generates the same braking force as the hydraulic brake. The reason for this is that the EWB implements self-energizing using a wedge phenomenon. That is, as the actuator is driven, the wedge is moved to press the pads and a frictional force between the pad and the disk serves as an additional input force. Even though the power of the motor is small, it is possible to generate a large braking force due to the wedge effect, which is caused by the wedge structure.
In addition, whenever an engine is started, the EWB has a function for compensating a clearance of the pad, that is, a function for moving the wedge assembly toward the pad to adjust a clearance between the pad and the disk, which deviates from a set value due to abrasion, so as to always maintain a set clearance of the pad.
Further, the EWB also has a Fail-Safe function, that is, a function for releasing a braking force applied to the disk to prevent an abnormal operation of a vehicle occurring when a braking force is not released and continuously applied during brake-fail.
In addition, the EWB can implement an EPB (Electric Parking Brake) function.
The EWB implements various additional functions such as a function for maintaining a set clearance of a pad, a Fail-Safe function, and an EPB function in addition to a main braking function. For this reason, the entire structure of the EWB becomes complicated. In particular, since the EWB uses a motor for implementing a braking function and another motor for implementing various additional functions, the EWB requires at least two motors.
Since the EWB uses two motors to separately generate power, the size of the EWB cannot help being increased due to a space for a motor. The increase in size causes limitation in assembling the EWB at the wheel.